'Poisonous Plants 1-2-1' video

This short video summarising the story of the giant hogweed is just one of
a series.

Family

Apiaceae

Giant hogweed in flower

Meaning of the Name

Heracleum
Named for Hercules. Literally, ‘belonging to Hercules’. Some sources
say this is simply because of its great size but others suggest that
Hercules derived his healing abilities from the plant. There are
about sixty species in the genus but none is especially known for
having medicinal properties.

mantegazzianum
Named for Paolo Mantegazza, 19th century Italian anthropologist and
ethnographist who is credited, by some, with being the first person
to extract cocaine from coca leaves.

Common Names and Synonyms

How Poisonous, How Harmful?

The speckled stem of a giant hogweed

The plant contains furocoumarins (psoralens) which produce
changes in the cell structure of the skin reducing its protection
against the effects of UV radiation. These can be released
from the plant simply by brushing against it. Exposure to sunlight
after contact causes severe skin rashes and/or blistering and burns
but the effects may not start until about twenty four hours after
contact. It may take several years for the skin to return to normal
during which time any renewed exposure to even quite dull daylight
will produce new burns.

Depending on the extent of the contact, the victim may suffer a
reddening of the skin, blisters or burns requiring hospital
treatment.

In some cases, a permanent change in skin pigmentation occurs.

Whenever Heracleum mantegazzianum is being discussed there
will be those who claim that the case against it is over-stated
and that many other plants are more dangerous. That point of
view seems to be opposed to the findings of a
1996 Swiss study
of 29 years of plant poisoning reports. Though only 18 reports
in that time concerned giant hogweed producing 'serious'
consequences that made it the second most dangerous plant with
only
Atropa belladonna,
deadly nightshade, at 42 cases, exceeding it.

Video Clip

Click to watch a short YouTube video produced and narrated by
John Robertson.

Heracleum mantegazzianum - the Sequel

The video above was made in June 2008.

This video contains footage from May 2009 and shows just how hard eradication of giant hogweed is.

Incidents

Heracleum sphondylium, cow parsnip,
common hogweed.
A common and much less troublesome
relative of giant hogweed

Typical contact comes from brushing through a stand of plants
when found on a riverbank, strimming a patch of rough ground in
early spring without realising that the young plant is present and
even contact with pets which have had contact with the plant.

In the summer of 2015, reports of a couple of children
suffering very nasty burns to their hands and arms led to a
number of other reports in the press. There were calls for more
action by government and local authorities. Edinburgh City
Council was one of those who assured the public it was doing
everything it could to control the plant - all evidence to the
contrary. There was a report of compensation being paid by one
private landowner to someone who came into contact with the
plant on his land. It must be expected that this will lead to
further claims.

As always, it is impossible to know if there were genuinely
more incidents in 2015 or whether the incidents that happened
were more likely to be reported than in previous years. The
plant's science is not well enough understood to be able to say
whether 2015 was an especially bad year or, if the plants were
more harmful, why that was.

A man who had stripped to the waist whilst strimming a patch of
rough ground suffered numerous small spot burns where he was hit by
spray from the strimmed plant. He reported suffering the burns
again two years later after removing his shirt on a hot day.

There are numerous anecdotes of children using the hollow stems as
peashooters and suffering burns around the mouth.

Though cattle and sheep are used to graze off the very
young shoots animals can be affected by the plant. There are a few
accounts of dogs suffering burns after contact so animals should be
kept away from larger plants.

A woman, in her fifties, showed pigmentation scars resulting from
contact with giant hogweed when she was seven.

A man still had visible scars fourteen years after hogweed burns.

On the walk where I saw the plants featured in the second video,
above, a friend slashed at a plant with his walking pole. I was
struck, just above the mouth, by a single drop of juice but that was
enough to give a small red spot which reappears on sunny days.

The confusion which can be caused by common names was ably
illustrated by an online discussion following a news story about
Heracleum mantegazzianum in part of Canada. Some commenters claimed
the plant was not as harmful as people said, apparently confusing
the sphondylium species with the giant hogweed. One even wrote about
its many medicinal properties before it became clear he was talking
about an entirely different genus.

There was also a lot of discussion about whether this was a new
problem and how bad its effects might be. Both points were answered
by one poster who remembered, about 30 years ago, playing with his
brother, in a field of giant hogweed. The effects started to appear
the following day and, within a week, they 'looked liked two mini
elephant men...[and] had seeping water sacks hanging off of us for a
long time.' He clearly remembered repeated burning for several years
after and said his skin is still discoloured.

Heracleum mantegazzianum growing in Edinburgh.
In the top right corner is a McDonald's sign.

In spring 2010, I spotted a piece of derelict land, within the
boundaries of the Fort Kinnaird Shopping Centre, in Edinburgh, which
was almost completely covered in giant hogweed. The land is just
across the road from a large DIY superstore, B & Q, and within sight
of the fast food restaurants serving the area.

With no fencing around this piece of land, there is a real risk
of someone suffering serious harm if they do not know what the plant
is. As the picture shows, the plants are already overgrowing the
pavement so someone just walking along the road could brush against
it.

Edinburgh City Council say that all they can do is offer the
landowner advice on removal, that is assuming they can find out who
owns the land. They do not have the power to order the land to be
fenced off.

A visit to Edinburgh, in July 2010, revealed why I failed to get
Edinburgh City Council interested in this small plot of land. The
whole city was blanketed in giant hogweed. Without stopping the car
or turning off one of the main feeder roads into the city centre, we
spotted at least six sites where giant hogweed was thriving and, in
many cases already setting seed. In 2012, the situation was as bad,
if not worse, and you can follow the links above to see photo-blog
entries showing plants in Edinburgh.

In July 2012, the Portadown Times reported on some teenage boys
who had suffered severe burns after contact with giant hogweed. The
paper kindly gave permission for photos of the boys to be reproduced
on this site.

Copyright 2012, the Portadown Times. Used with permission.

Folklore and Facts

There is a theory that plants produce furocoumarins as a
defence against attacks from a root fungus. Anyone suffering
burns is, therefore, suffering 'collateral damage'. The theory
could explain why other genera and species will, sometimes,
cause similar problems but only sometimes. My thought is that,
perhaps, the Heracleum mantegazzianum was not exposed to this
fungus in its native territory and still over-reacts to a fungal
attack resulting in the excessive output of the chemicals. That
might, also, explain why the plant importers seem to have been
unaware of the problems the plant could cause.

These will have to remain speculative unless anyone is
willing to fund detailed research into the issue.

Heracleum mantegazzianum,
giant hogweed

It was introduced to the UK by the Victorians who thought its
size would make a dramatic statement in large gardens. It escaped
and has spread rapidly to be a major problem on river banks in some
areas. The Wildlife and Countryside Act 1981 makes it an offence to
plant or cause giant hogweed to grow in the wild. In July 2003, the
Daily Telegraph reported that an EU funded programme was looking at at bringing fungi from Russia to attack the plant.
No further information has been found on this project but, in a 2010
publication, the Northern Ireland Department of Agriculture and
Rural Development says that a range of fungi has been found to be
associated with the plant but that they had to found to have
insignificant effects on its growth. This leaflet simply says that
no biological control is available.

Each giant hogweed plant is capable of producing about 50,000
seeds and, though they only drop close to the plant, they can be
transported on shoe soles to other areas. The seeds remain viable
for seven years meaning that eradication is a long and expensive
process. After spending £250,000 in two years it was claimed that
there was no flowering giant hogweed on the river Tweed in 2005.
Since then, annual spraying in the spring is undertaken to keep the
plant down. Sadly, the plants shown in the two videos above were filmed on
the River Tweed network in May 2008 and 2009.

One of many hundreds of giant hogweed
plants in Edinburgh

The only alternative to a seven year programme of spraying is to
completely remove the topsoil which may contain the seeds. Complete
removal with a guarantee that it won’t return cost £20,000 for an
area described as not much bigger than a small town garden.

Though the Heracleum sphondylium, cow parsnip or common
hogweed, is very less frequently a cause of problems it does
produce the same chemicals as giant hogweed. Not enough is known
about the conditions required to increase the concentration of
the furocoumarins to the point where harm can occur but, it
would appear, that strong sunlight is required for the ordinary
hogweed to produce burning.